There is a need for simple diagnostic tests for common diseases that can be executed by untrained personnel. Simpler tests would allow for home or doctor's office testing when current procedures require the analysis to be done by an outside laboratory. Possible benefits of simpler tests are decreased turnaround time and a reduction in cost. Representative examples are home pregnancy and glucose testing.
A common format for the simplified tests is the immunostrip format which comprises a solid support through which the reagents used in the test can flow by capillarity. Usually this format contains a mobile phase consisting of the test solution and an optically labeled, analyte-specific binding partner. The analyte binds to the optically labeled, analyte-specific binding partner and passes through a capture zone which contains a capture-analyte immobilized thereon. Where the capture-analyte is an analyte modified so that it can be immobilized on the capture zone of the immunostrip. The typical optical labels are gold sol or colored particles such as latex particles although other optical labels such as dye filled liposomes may be used. While optical, i.e. visually detectable, labels are preferred, this type of strip format can employ other types of detectable labels such as enzymes when the capture zone contains a substrate for the enzyme label. The capture zone captures excess labeled, analyte-specific binding partner as the labeled, analyte-specific binding partner which has combined with analyte to form an analyte/labeled specific binding partner conjugate migrates to a detection zone where the conjugate is detected.
Other formats are possible and may be advantageous. For example, it may be preferable to allow the capture-analyte to mix with the test solution before the mixture contacts the labeled, analyte-specific binding partner such that the capture-analyte and the analyte in the test solution simultaneously compete to react with the labeled, analyte-specific binding partner. The resulting mixture then migrates to the capture zone where the capture-analyte labeled analyte-specific binding partner complex and the unbound capture-analyte are captured in the capture zone. The analyte-labeled, analyte specific binding partner complex and the unbound labeled, analyte-specific binding partner continue to migrate to the detection zone where they are captured. Another example involves placing the capture-analyte in a separate zone where the capture-analyte is not immobilized so that the analyte in the test solution is allowed to first bind with the labeled analyte-specific binding partner. The mixture then migrates to the capture-analyte zone where the unbound, labeled analyte-specific binding partner is bound to the capture analyte. The final mixture migrates to the capture zone where the capture-analyte labeled, analyte-specific binding partner complex and the unbound capture-analyte are captured. The analyte-labeled, analyte-specific binding partner complex and the unbound, labeled, analyte-specific binding partner continue to migrate to the detection zone where they are captured. In a third example, the labeled, analyte-specific binding partner is mixed with the capture-analyte to form a labeled, analyte-specific binding partner complex and placed in a labeled, analyte-specific binding partner zone. When the test solution is brought into contact with the test device, the analyte in the test solution competes with the free capture-analyte to bind to the labeled, analyte-specific binding partner after which the resulting mixture migrates to the capture zone where the capture-analyte labeled, analyte-specific binding partner complex and the unbound capture-analyte are captured in the capture zone. The analyte-labeled analyte-specific binding partner complex and the unbound labeled, analyte-specific binding partner continue to migrate to the detection zone where they are captured.
In all three of the above examples, the capture-analyte is not immobilized in the test device. After the test device is contacted with the test solution, the mixture containing the labeled, analyte-specific binding partner bound to the analyte from the test solution the labeled, analyte-specific binding partner bound to the capture-analyte and the unbound capture-analyte flow to the capture zone by capillarity where the labeled, analyte-specific binding partner bound to the capture-analyte and the unbound capture-analyte compete to bind the binding reagent immobilized in the capture zone. The binding reagent is a reagent capable of binding the solid support and the capture-analyte. The labeled, analyte-specific binding partner which is not bound to the analyte moves through the capture zone, to the detection zone, and is collected by the detection reagent.
In a fourth example, the capture-analyte is immobilized by a binding reagent in the capture zone in the test device. When the test device is in contact with the test solution, the analyte in the test solution is allowed to be in contact with and bind to the labeled, ananlyte-specific binding partner first whereupon the mixture moves to the capture zone where the analyte-unbound labeled, analyte-specific binding partner is captured by the immobilized capture-analyte. The uncaptured labeled, analyte-specific binding partner then moves to the detection zone and is collected by the detection reagent. The labeled, analyte-specific binding partner binds to the capture-analyte reagent in inverse relationship to the concentration of the analyte in the test solution.
The capture-analyte and analyte binding competition for the optically labeled analyte binding partner can be variable with regard to the binding rate and the binding strength and may require variable contact times before reaching the capture zone. These formats provide alternative contact times.
There are numerous analytes whose simplified determination could be of benefit. Examples of such analytes include digoxin, thyroxine, drugs of abuse such as cocaine, and anticonvulsants such as phenobarbitol. By using the bone resorption marker deoxypyridinoline (DPD), as an illustrative example it is the intent of this invention to describe binding label-amino acid analyte reagents which act as capture-analytes to provide access to alternative formats for immobilizing an analyte onto the capture zone of an immunostrip.